1. Field of the Invention
The present invention relates to an electrohydraulic system for controlling a hydraulically actuated clutch arranged between an internal combustion engine and a transmission associated with the engine and, more particularly, to hydraulic emergency control means for controlling the clutch, especially in the event of failure of an electric supply for the electrohydraulic control system for the clutch.
2. Description of the Related Art
A hydraulic emergency control for a hydraulically actuated clutch arranged between an internal combustion engine and a transmission is known from EP 0 728 265 B1. This hydraulic emergency control is part of an electrohydraulic clutch control system having at least one pump driven by the internal combustion engine for feeding at least one work line. At least one fixed or variable choke is arranged in the at least one work line. At least one valve constructed as a switching valve is provided for controlling the clutch at least in the event of failure of the electric supply of the electrohydraulic clutch control. A first control line is connected with a first control input of the switching valve and is connected, in front of the choke with respect to the feed direction, with the work line. A second control is connected with a second control input of the switching valve and, behind the choke with respect to the feed direction, with the work line.
Further, a 4/2-directional valve is provided in the second control line and acts upon a spring-loaded accumulator communicating with a line leading to the clutch. The switching valve controls a clutch pressure valve that communicates with the clutch via a line. Another choke with a check valve is provided in this line. The construction of this hydraulic emergency control is therefore quite complicated. In the event of outage of the electric supply for the clutch control, the clutch pressure valve sets the maximum clutch pressure. Because of the accumulator and choke, the clutch pressure does not rise suddenly, but rather slowly along a fixed ramp As a result of this arrangement, a variable change in the dutch pressure increase is not possible, so that the closing of the clutch is also not variable. However, since a variable closing of the clutch is desired or required depending on the respective start situationxe2x80x94starting on an ascending or descending grade, for examplexe2x80x94the closing of the clutch may cause discomfort or inconvenience in many situations.
It is an object of the present invention to provide a hydraulic system for a hydraulically actuated clutch arranged between the internal combustion engine and its transmission, which is part of the electrohydraulic clutch control system and which includes a hydraulic emergency control means, that does not suffer from the above-described disadvantage.
According to the invention the hydraulic system for a hydraulically actuated clutch arranged between an internal combustion engine and a transmission, which is part of an electrohydraulic clutch control system for the clutch and which includes hydraulic emergency control means, comprises
a pump driven by the internal combustion engine and delivering pressurized fluid to a work line;
a throttle valve in the work line;
a regulating valve having an output port connected to the clutch by a clutch line, which controls the clutch upon failure of an electrical supply for the electrohydraulic clutch control system;
a first control line connected to the work line upstream of the throttle valve and to a first control input of the regulating valve;
a second control line connected to the work line downstream of the throttle valve and to a second control input of the regulating valve;
a third control line connected to the clutch line and to a third control input of the regulating valve;
wherein, when pressure in the first control line increases faster than pressure in the second control line, an opening cross section between a pressure port and the output port increases.
The hydraulic emergency control according to the invention for a hydraulically actuated clutch arranged between an internal combustion engine and a transmission has the advantages that its construction is substantially simpler due to the use of a regulating valve for controlling the clutch and that a variable closing of the clutch is possible.
The construction of the hydraulic emergency control is particularly simple when the working connection of the regulating valve is connected with the clutch by at least one clutch line and does not act on another valve for controlling the clutch. The regulation of the clutch pressure is simplified, particularly by a return line of the first regulating valve that is connected with the clutch line and a control input of the regulating valve. In particular, it is advantageous when the return line is connected with a second control input of the regulating valve A definite position of the regulating valve can be reached when a restoring spring or return spring is arranged at a control input of the regulating valve. This return spring can be arranged at the first or second control input of the regulating valve. When the first control input of the regulating valve is electrically or hydraulically controllable, the regulating valve can also be advantageously used in normal operation for controlling the clutch, so that a separate regulating valve for controlling the clutch in normal operation can be eliminated. It is advantageous when the choke is directionally switchable electrically or hydraulically in normal operation and can be switched on via a spring if the electric supply fails.
Further advantages and advantageous further embodiments of the hydraulic emergency control according to the invention for a hydraulically actuated clutch arranged between an internal combustion engine and a transmission are described in the appended dependent claims and the following description.